I run two 5K LG displays (in addition to the laptop screen) on the 16” and don’t have the issue.

I believe this is correct.

I have always ran a 4K monitor and never hit this issue. My 15" (2018) and 16" MacBook Pro run silent when connected to the 4K monitor as it uses 2x scaling by default (so 4K "looks like" 1080p).

However if I connect a 1440p display after half an hour or so the fans kick in.

I don't own a 1440p display anymore to test this solution unfortunately.

I've used on LG 4K, AOC 4K monitors running at 3840 x 2160 and they all have the similar fan problems. MBP 16 is 5500M

I'm running one of the mentioned GPUs on a 4k monitor and never saw this problem.

Seems like a good excuse to update my monitor lol - any recommendations?

I think it's specific to 1440p